Odd Woofers in these Mini 7s

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#2
I'm not sure from the photo because the grill is in place, but they look very much like mine (1977-78). The woofer cone wasn't black, but rather a lighter tone paper.
Remember that over the lenghty period of time that they were being sold that there were different configurations (example: sealed *and* ported) plus several different sources for the woofers and perhaps the tweeters as well. Radio Shack was terrible about changing components, as well as drivers, and never documenting or designating the changes.

Best Regards,
TerryO
 
#3
The woofer cone wasn't black, but rather a lighter tone paper..
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Are these the ones you refer to? See the pictures.

(((FYI, The reason I bought a dozen of these nice and good performing 4" bass drivers back in 1985 were to do experiment with bookshelf de-correlated bass arrays, a 2. (1+2) system.

I’m still using them corner placed in two rows, together with a TL sub (XO at 50 Hz/ 12 dB octave) placed centrally in the same bookshelf that covers entirely one of the short walls.
See the skeleton of the TL bookshelf sub I built –91 used with various sub drivers, latest and best performer a Peerless 10” 830842 bought when the driver was preliminary new and factory released.

Using L+R or L-R signals variable delayed (typically 5-40 mS depending on the recorded definition) and mixed, weighted with ordinary L+R or L-R to counter weight any destructive bass interference at the listening point from the main sub is defeated or lowered as the arrays form a 1(L array) + 2(sub) + or -1(R array) weighted straight or bessel array for signals below about 78 Hz (array c-c= 2.2m = lambda/2).

The arrays are filtered with a 3 dB slope from 50 Hz i.e. 100 to about 800 Hz at a level suitable for the definition of the recorded material, -6 dB or lower and really, in my opinion makes a real difference for most of my vinyl or cd recordings.

When comparing the soundstage with the preceding set-up the 2.1 system only i.e. the bookshelf-sub and bookshelf mains L + R with the 2. (1+2) system none of my friends prefer the former set-up and I agree too, especially when playing concerts, chorals or old Jazz stereo or mono recordings.)))

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#8
To me it looks like the dust cap is smaller and the surround is thicker and juts forward more than my Mini 7. Most of the Mini 7's I've seen use the Woofer Bjorno has. ( didn't know they sold the woofer separate, my RS DIY 4 inch Woofers are noticeably different from the Mini 7 Woofer).
 
#10
Ive been looking for it...
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Sorry, I can’t help you with the T/S data, but believe this woofer had a high Qts and rather low x-max thus only suitable for OB/IB applications.

Here is a link to a guy who has some experience with this driver:

http://homepage.mac.com/dero72/speakers/subwoofers.html

He wrote:

Then I bought best the woofer available at radio-shack, 40-8424. It was of much better construction than the first but it really had parameters “weird” what made any design realistic impossible: Ideal volume would have been of 30 foot-cubic - as large as two large freezers! With my cabinet of only 6 foot-cubic, the agreement was far from being perfect, and the answer was rather disappointing, that is to say a point -3dB with 38 Hz. I thus replaced the passive filter by an active filter of construction house. I thus could dope the crossover by choosing a very low cut-off frequency, towards 25 Hz, which transformed indeed the crossover into equalizing to create an assisted system. I also benefited from it to cover the outside of the cabinet with grey carpet disco music. This system was satisfactory for a time but possibly, I wanted still better. It was also my departure of the Radio-Shack products!
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